Isolated discrete forward DC/DC design: Page 5 of 5

June 24, 2016 // By Bruce Haug
Isolated discrete forward DC/DC design
High density isolated DC/DC converters have significantly changed during the course of the past 25 years. The introduction of the full and half-brick form factors back then created a rush to use them in distributed power architectures in telecom, datacom, industrial and medical systems where a bus voltage is routed to every board within a system and each board had its own isolated DC/DC converter.

The LT8302 eliminates the need for an optocoupler or extra transformer winding by sensing the output voltage on the primary-side of the transformer. The output voltage is accurately measured at the primary-side switching node waveform during the off time of the power transistor as shown in figure 4, where N is the turns ratio of the transformer, VIN is the input voltage and VC is the maximum clamped voltage.

Fig. 4: Typical switch node waveform.

Transformer selection and design considerations for the LT8302

The transformer specification and design is probably the most critical part of successfully applying the LT8302. In addition to the usual list of caveats dealing with high frequency isolated power supply transformer design of having a low leakage inductance and close coupling, the transformer turns ratio must be tightly controlled. Linear Technology has worked with several magnetic component manufactures to produce pre-designed flyback transformers for use with the LT8302.


About the author:


Bruce Haug is Senior Product Marketing Engineer, Power Products at Linear Technology –

Design category: 

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